Mellie wants to find out if doing laughter therapy decreases stress hormone levels. She has half of her sample participate in a laughter therapy group session and the other half participate in a talk therapy group session. After the sessions, she takes blood samples from all of the participants and analyzes them for stress hormones. Mellie's study used the _____ method.

a. observational
b. survey
c. experimental
d. quasi-experimental

Answer: c. experimental